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Biomedical subjects

B Schuster

Publications and source records attributed to B Schuster.

At least 19 recordsLinked to original sources
PubMed2006

Chemosensory specific reduction of trigeminal sensitivity in subjects with olfactory dysfunction.

Humans with olfactory loss have been found to exhibit a decreased sensitivity of the chemosensory trigeminal system. It is not clear, whether the reduced trigeminal sensitivity is restricted to the chemosensitive properties of the trigeminal nerve, or whether it reflects a general decrease of trigeminal sensitivity which is also found for cutaneous afferents. To investigate the relationship between cutaneous somatosensory and intranasal chemosensory trigeminal sensitivity, 91 subjects were investigated. Forty-five of them were considered healthy controls, whereas 46 subjects had olfactory dysfunction. Subjects with olfactory dysfunction were found to have higher thresholds for CO2 than controls indicating lower trigeminal chemosensory sensitivity in subjects with olfactory dysfunction. Both etiology and degree of olfactory dysfunction appeared to have an impact on CO2 thresholds. In contrast, no such differences were found with regard to detection thresholds for electrical cutaneous stimulation. These results indicate that the decrease of trigeminal sensitivity in subjects with olfactory dysfunction is specific for chemosensory sensations.

Adult↗
PubMed2006

Subjects with congenital anosmia have larger peripheral but similar central trigeminal responses.

Most odorants not only stimulate olfactory receptor neurons but also activate the intranasal trigeminal nerve. The simultaneous activation of the olfactory and the trigeminal system leads to an interaction in the brain. Therefore, assessment of the trigeminal impact of odorants may be difficult in subjects with a normal sense of smell. To obtain a deeper insight into both, mechanisms of changes in trigeminal sensitivity in anosmic patients and interactions between the olfactory/trigeminal systems in healthy subjects, 21 patients with isolated congenital anosmia (ICA) were investigated in this series of explorative, hypothesis-generating experiments and compared with 35 healthy controls. Trigeminal sensitivity was measured by psychophysical (lateralization task, intensity ratings) and electrophysiological (trigeminal event-related potential, negative mucosal potential) means. ICA patients were found to have higher peripheral activation than controls. On central levels, however, similar responsiveness to trigeminal stimuli was found in ICA patients when compared with healthy subjects. The results of the study are discussed by proposing a model of mixed sensory adaptation/compensation in the interactions between olfactory and the trigeminal system.

Adolescent↗
PubMed2006

S-layer proteins as key components of a versatile molecular construction kit for biomedical nanotechnology.

Surface (S)-layer proteins and S-layer fusion proteins incorporating functional sequences, self-assemble into monomolecular lattices on solid supports and on various lipid structures. Based on these S-layer proteins, supramolecular assemblies can be constructed which are envisaged for label-free detection systems, as affinity matrix, as anti-allergic immuno-therapeutics, as membrane protein-based screening devices, and as drug targeting and delivery systems.

Anti-Allergic Agents↗
PubMed2004

Functionalisation of surfaces with S-layers.

Two-dimensional bacterial surface layer protein crystals (S-layers) are the most commonly observed cell surface structures in prokaryotic organisms (bacteria and archaea). Isolated S-layer proteins have the intrinsic tendency to self-assemble into two-dimensional arrays in suspension and at various interfaces. Basic research on the structure, genetics, chemistry, morphogenesis and function of S-layers has led to a broad spectrum of applications in molecular nanotechnology and biomimetics. The possibility to change the natural properties of S-layer proteins by genetic manipulation opens new ways for the tuning of their structural and functional features. Functionalised S-layer proteins that maintain their propensity for self-assembly have led to new affinity matrices, diagnostic tools, vaccines or biocompatible surfaces, as well as to biological templating or specific biomineralisation strategies at surfaces.

Journal Article↗
PubMed2001

What did we learn about national organizational collaboration at the advisory committee level?

This article provides an overview of the typical roles and tasks of advisory groups in general, followed by a discussion of the roles and tasks the Interdisciplinary Generalist Curriculum (IGC) Project Advisory Committee was asked to assume and how these were fulfilled. It analyzes the lessons learned about advisory committees as a result of the IGC Project experience. Key elements of success in fulfilling advisory committee obligations include well-defined expectations, periodic evaluations, and clear communication between project leadership and the members of the advisory committee. In the spirit of lessons learned from the IGC Project, this critique identifies several philosophical and logistic issues that might be considered in the design and implementation of future projects, such as the need to choose committed, high-energy advisory committee members who are willing to perform many complex, time-consuming tasks.

Curriculum↗
PubMed2001

Phase 2 trial of WR6026, an orally administered 8-aminoquinoline, in the treatment of visceral leishmaniasis caused by Leishmania chagasi.

There are no recognized orally administered treatments for any of the leishmaniases. The 8-aminoquinoline WR6026 is an orally administered analog of primaquine that cured 50% of patients with kala-azar in Kenya at a dose of 1 mg/kg/day for 28 days. A further phase 2, open-label, dose-escalating safety and efficacy study was performed for kala-azar in Brazil. Cure rates for Brazilian patients treated for 28 days were as follows: 1 mg/kg/day: 0 of 4 (0%); 1.5 mg/kg/day: 1 of 6 (17%); 2.0 mg/kg/day: 4 of 6 (67%); 2.5 mg/kg/day: 1 of 5 (20%); and 3.25 mg/kg/day: 0 of 1 (0%). Nephrotoxicity that was not anticipated from preclinical animal studies or from phase 1 studies was seen at 2.5 mg/kg/day in 2 patients and in the single patient administered 3.25 mg/kg/day. WR6026 demonstrated the unusual clinical features of lack of increased efficacy against Brazilian kala-azar with increased dosing above 2 mg/kg/day and toxicity that was not present in previous investigations.

Administration, Oral↗
PubMed2000

S-layer-supported lipid membranes.

Many prokaryotic organisms (archaea and bacteria) are covered by a regularly ordered surface layer (S-layer) as the outermost cell wall component. S-layers are built up of a single protein or glycoprotein species and represent the simplest biological membrane developed during evolution. Pores in S-layers are of regular size and morphology, and functional groups on the protein lattice are aligned in well-defined positions and orientations. Due to the high degree of structural regularity S-layers represent unique systems for studying the structure, morphogenesis, and function of layered supramolecular assemblies. Isolated S-layer subunits of numerous organisms are able to assemble into monomolecular arrays either in suspension, at air/water interfaces, on planar mono- and bilayer lipid films, on liposomes and on solid supports (e.g. silicon wafers). Detailed studies on composite S-layer/lipid structures have been performed with Langmuir films, freestanding bilayer lipid membranes, solid supported lipid membranes, and liposomes. Lipid molecules in planar films and liposomes interact via their head groups with defined domains on the S-layer lattice. Electrostatic interactions are the most prevalent forces. The hydrophobic chains of the lipid monolayers are almost unaffected by the attachment of the S-layer and no impact on the hydrophobic thickness of the membranes has been observed. Upon crystallization of a coherent S-layer lattice on planar and vesicular lipid membranes, an increase in molecular order is observed, which is reflected in a decrease of the membrane tension and an enhanced mobility of probe molecules within an S-layer-supported bilayer. Thus, the terminology 'semifluid membrane' has been introduced for describing S-layer-supported lipid membranes. The most important feature of composite S-layer/lipid membranes is an enhanced stability in comparison to unsupported membranes.

Bacterial Proteins↗
PubMed1999

Microphase separation in low density lipoproteins. Evidence for a fluid triglyceride core below the lipid melting transition.

The structural organization of the neutral lipid core in human low density lipoproteins (LDL) was investigated in physicochemically defined, distinct human LDL subspecies in the density range of 1. 0244-1.0435 g/ml by evaluation of the core lipid transition temperature, chemical composition, and the behavior of spin-labeled core lipids. Calorimetric studies were performed on more than 60 LDL preparations, and the transition temperature, which varied between 19 and 32 degreesC, was correlated to the chemical composition and revealed a discontinuity at a critical cholesteryl ester to triglyceride ratio of approximately 7:1. For electron spin resonance studies, several LDL preparations were probed with spin-labeled cholesteryl esters and triglycerides, respectively. In LDL with a high triglyceride content, both labels exhibited similar mobility behavior. In contrast, in LDL with only small concentrations of triglycerides, the behavior of labeled cholesteryl esters and labeled triglycerides differed distinctly. The cholesteryl esters were strongly immobilized below the transition temperature, whereas the triglycerides remained fluid throughout the measured temperatures. These results suggest that the critical cholesteryl ester to triglyceride mass ratio of 7:1 corresponds to two concentric compartments with a radial ratio of 2:1, where the liquid triglycerides occupy the core, and the cholesteryl esters form the frozen shell. At higher triglyceride contents, the triglyceride molecules insert into the cholesteryl ester shell and depress the peak transition temperature of the LDL core, whereas at lower triglyceride contents, excess cholesteryl esters are dissolved in the core.

Calorimetry, Differential Scanning↗
PubMed1999

Probing the stability of S-layer-supported planar lipid membranes.

Isolated protein subunits of the crystalline bacterial cell surface layer (S-layer) of Bacillus coagulans E38-66 have been recrystallized on one side of planar black lipid membranes (BLMs) and their influence on the electrical properties, rupture kinetics and mechanical stability of the BLM was investigated. The effect on the boundary potential, the capacitance or the conductance of the membrane was negligible whereas the mechanical properties were considerably changed. The mechanical stability was characterized by applying voltage pulses or ramps to induce irreversible rupture. The amplitude of the voltage pulse leading to rupture allows conclusions on the ability of membranes to resist external forces. Surprisingly, these amplitudes were significantly lower for composite S-layer/lipid membranes compared to undecorated BLMs. In contrast, the delay time between the voltage pulse and the appearance of the initial defect was found to be drastically longer for the S-layer-supported lipid bilayer. Furthermore, the kinetics of the rupture process was recorded. Undecorated membranes show a fast linear increase of the pore conductance in time, indicating an inertia-limited defect growth. The attachment of an S-layer causes a slow exponential increase in the conductance during rupture, indicating a viscosity-determined widening of the pore. In addition, the mechanical properties on a longer time scale were investigated by applying a hydrostatic pressure across the BLMs. This causes the BLM to bulge, as monitored by an increase in capacitance. Compared to undecorated BLMs, a significantly higher pressure gradient has to be applied on the S-layer face of the composite BLMs to observe any change in capacitance.

Bacillus↗
PubMed1999

The effect of S-layer protein adsorption and crystallization on the collective motion of a planar lipid bilayer studied by dynamic light scattering.

A dedicated dynamic light scattering (DLS) setup was employed to study the undulations of freely suspended planar lipid bilayers, the so-called black lipid membranes (BLM), over a previously inaccessible spread of frequencies (relaxation times ranging from 10(-2) to 10(-6) s) and wavevectors (250 cm(-1) < q < 38,000 cm(-1)). For a BLM consisting of 1,2-dielaidoyl-sn-3-glycero-phosphocholine (DEPC) doped with two different proportions of the cationic lipid analog dioctadecyl-dimethylammonium bromide (DODAB) we observed an increase of the lateral tension of the membrane with the DODAB concentration. The experimentally determined dispersion behavior of the transverse shear mode was in excellent agreement with the theoretical predictions of a first-order hydrodynamic theory. The symmetric adsorption of the crystalline bacterial cell surface layer (S-layer) proteins from Bacillus coagulans E38-66 to a weakly cationic BLM (1.5 mol % DODAB) causes a drastic reduction of the membrane tension well beyond the previous DODAB-induced tension increase. The likely reason for this behavior is an increase of molecular order along the lipid chains by the protein and/or partial protein penetration into the lipid headgroup region. S-layer protein adsorption to a highly cationic BLM (14 mol % DODAB) shows after 7 h incubation time an even stronger decrease of the membrane tension by a factor of five, but additionally a significant increase of the (previously negligible) surface viscosity, again in excellent agreement with the hydrodynamic theory. Further incubation (24 h) shows a drastic increase of the membrane bending energy by three orders of magnitude as a result of a large-scale, two-dimensional recrystallization of the S-layer proteins at both sides of the BLM. The results demonstrate the potential of the method for the assessment of the different stages of protein adsorption and recrystallization at a membrane surface by measurements of the collective membrane modes and their analysis in terms of a hydrodynamic theory.

Adsorption↗
PubMed1998

Self-assembled alpha-hemolysin pores in an S-layer-supported lipid bilayer.

The effects of a supporting proteinaceous surface-layer (S-layer) from Bacillus coagulans E38-66 on a 1,2-diphytanoyl-sn-glycero-3-phosphatidylcholine (DPhPC) bilayer were investigated. Comparative voltage clamp studies on plain and S-layer supported DPhPC bilayers revealed no significant difference in the capacitance. The conductance of the composite membrane decreased slightly upon recrystallization of the S-layer. Thus, the attached S-layer lattice did not interpenetrate or rupture the DPhPC bilayer. The self-assembly of a pore-forming protein into the S-layer supported lipid bilayer was examined. Staphylococcal alpha-hemolysin formed lytic pores when added to the lipid-exposed side. The assembly was slow compared to unsupported membranes, perhaps due to an altered fluidity of the lipid bilayer. No assembly could be detected upon adding alpha-hemolysin monomers to the S-layer-faced side of the composite membrane. Therefore, the intrinsic molecular sieving properties of the S-layer lattice do not allow passage of alpha-hemolysin monomers through the S-layer pores to the lipid bilayer. In comparison to plain lipid bilayers, the S-layer supported lipid membrane had a decreased tendency to rupture in the presence of alpha-hemolysin.

Bacillus↗
PubMed1998

Voltage clamp studies on S-layer-supported tetraether lipid membranes.

Isolated subunits from the cell surface proteins (S-layer) of Bacillus coagulans E38-66 have been recrystallized on a glycerol dialkyl nonitol tetraether lipid (GDNT)-monolayer and the electrophysical features of this biomimetic membrane have been investigated in comparison to unsupported GDNT-monolayers. The GDNT-monolayer, spread on a Langmuir-Blodgett trough, was clamped with the tip of a glass patch pipette. In order to investigate the barrier function and potential to incorporate functional molecules, voltage-clamp examinations on plain and S-layer-supported GDNT-monolayers were per-formed. Our results indicate the formation of a tight GDNT-monolayer sealing the tip of the glass pipette, and a decrease in conductance of the GDNT-monolayer upon recrystallization of the S-layer protein. Thus, the S-layer protein, apparently, did not penetrate or rupture the lipid monolayer. The valinomycin-mediated increase in conductance was less pronounced for the S-layer-supported than for the plain GDNT-monolayer, indicating differences in the accessibility and/or in the fluidity of the lipid membranes. Furthermore. in contrast to plain GDNT-monolayers. S-layer supported GDNT-monolayers with high valinomycin-mediated conductance persisted over long, periods of time, indicating enhanced stability. These composite S-layer/lipid films may constitute a new tool for electrophysical and electrophysiological studies on membrane-associated and membrane-integrated biomolecules.

Anti-Bacterial Agents↗
PubMed1998

Thermal stability of apolipoprotein B100 in low-density lipoprotein is disrupted at early stages of oxidation while neutral lipid core organization is conserved.

The time course of the unfolding characteristics of the protein moiety and of the thermotropic behavior of the core-located apolar lipids of highly homogeneous low-density lipoprotein (LDL) subspecies (d 1.030-1.040 g/mL) have been evaluated during transition metal- and azo radical-induced oxidation using differential scanning calorimetry. Apolipoprotein B100 (apo-B100) structure was highly sensitive to oxidative modification; indeed, a significant loss of thermal stability was observed at initial stages irrespective of whether oxidation was mediated by site-specific binding of copper ions or by free radicals generated during decomposition of azo compounds. Subsequently, thermal protein integrity was destroyed, as a result of potentially irreversible protein unfolding, cross-linking reactions, and aggregation. Our results suggest that even minimal oxidative modification of apo-B100 has a major impact on the stability of this large monomeric protein. By contrast, the core lipids, which consist primarily of cholesteryl esters and triglycerides and play a determinant role in the thermal transition occurring near physiological temperature, preserved features of an ordered arrangement even during propagation of lipid peroxidation.

Amidines↗
PubMed1997

Applications of S-layers.

The wealth of information existing on the general principle of S-layers has revealed a broad application potential. The most relevant features exploited in applied S-layer research are: (i) pores passing through S-layers show identical size and morphology and are in the range of ultrafiltration membranes; (ii) functional groups on the surface and in the pores are aligned in well-defined positions and orientations and accessible for binding functional molecules in very precise fashion; (iii) isolated S-layer subunits from many organisms are capable of recrystallizing as closed monolayers onto solid supports at the air-water interface, on lipid monolayers or onto the surface of liposomes. Particularly their repetitive physicochemical properties down to the subnanometer scale make S-layers unique structures for functionalization of surfaces and interfaces down to the ultimate resolution limit. The following review focuses on selected applications in biotechnology, diagnostics, vaccine development, biomimetic membranes, supramolecular engineering and nanotechnology. Despite progress in the characterization of S-layers and the exploitation of S-layers for the applications described in this chapter, it is clear that the field lags behind others (e.g. enzyme engineering) in applying recent advances in protein engineering. Genetic modification and targeted chemical modification would allow several possibilities including the manipulation of pore permeation properties, the introduction of switches to open and close the pores, and the covalent attachment to surfaces or other macromolecules through defined sites on the S-layer protein. The application of protein engineering to S-layers will require the development of straightforward expression systems, the development of simple assays for assembly and function that are suitable for the rapid screening of numerous mutants and the acquisition of structural information at atomic resolution. Attention should be given to these areas in the coming years.

Bacteria↗
PubMed1995

The mechanism of action of phenylalanine ammonia-lyase: the role of prosthetic dehydroalanine.

Phenylalanine ammonia-lyase (EC 4.3.1.5) from parsley is posttranslationally modified by dehydrating its Ser-202 to the catalytically essential dehydroalanine prosthetic group. The codon of Ser-202 was changed to those of alanine and threonine by site-directed mutagenesis. These mutants and the recombinant wild-type enzyme, after treatment with sodium borohydride, were virtually inactive with L-phenylalanine as substrate but catalyzed the deamination of L-4-nitrophenylalanine, which is also a substrate for the wild-type enzyme. Although the mutants reacted about 20 times slower with L-4-nitrophenylalanine than the wild-type enzyme, their Vmax for L-4-nitrophenylalanine was two orders of magnitude higher than for L-phenylalanine. In contrast to L-tyrosine, which was a poor substrate, DL-3-hydroxyphenylalanine (DL-m-tyrosine) was converted by phenylalanine ammonia-lyase at a rate comparable to that of L-phenylalanine. These results suggest a mechanism in which the crucial step is an electrophilic attack of the prosthetic group at position 2 or 6 of the phenyl group. In the resulting carbenium ion, the beta-HSi atom is activated in a similar way as it is in the nitro analogue. Subsequent elimination of ammonia, concomitant with restoration of both the aromatic ring and the prosthetic group, completes the catalytic cycle.

Alanine↗
PubMed1995

Core lipid structure is a major determinant of the oxidative resistance of low density lipoprotein.

The influence of thermally induced changes in the lipid core structure on the oxidative resistance of discrete, homogeneous low density lipoprotein (LDL) subspecies (d, 1.0297-1.0327 and 1.0327-1.0358 g/ml) has been evaluated. The thermotropic transition of the LDL lipid core at temperatures between 15 degrees C and 37 degrees C, determined by differential scanning calorimetry, exerted significant effects on the kinetics of copper-mediated LDL oxidation expressed in terms of intrinsic antioxidant efficiency (lag time) and diene production rate. Thus, the temperature coefficients of oxidative resistance and maximum oxidation rate showed break points at the core transition temperature. Temperature-induced changes in copper binding were excluded as the molecular basis of such effects, as the saturation of LDL with copper was identical below and above the core transition. At temperatures below the transition, the elevation in lag time indicated a greater resistance to oxidation, reflecting a higher degree of antioxidant protection. This effect can be explained by higher motional constraints and local antioxidant concentrations, the latter resulting from the freezing out of antioxidants from crystalline domains of cholesteryl esters and triglycerides. Below the transition temperature, the conjugated diene production rate was decreased, a finding that correlated positively with the average size of the cooperative units of neutral lipids estimated from the calorimetric transition width. The reduced accessibility and structural hindrance in the cluster organization of the core lipids therefore inhibits peroxidation. Our findings provide evidence for a distinct effect of the dynamic state of the core lipids on the oxidative susceptibility of LDL and are therefore relevant to the atherogenicity of these cholesterol-rich particles.

Calorimetry, Differential Scanning↗